Nonspecific sarcolemmal cation channels are critical for the pathogenesis of malignant hyperthermia

Malignant hyperthermia (MH) susceptibility has been attributed to a leaky sarcoplasmic reticulum (SR) caused by missense mutations in RYR1 or CACNA1S, and the MH crisis has been attributed solely to massive self-sustaining release of Ca²⁺ from SR stores elicited by triggering agents. Here, we show in muscle cells from MH-RyR1^R163C knock-in mice that increased passive SR Ca²⁺ leak causes an enlarged basal influx of sarcolemmal Ca ²⁺ that results in chronically elevated myoplasmic free Ca ²⁺ concentration ([Ca²⁺]_i) at rest. We discovered that Gd⁺³ and GsMTx-4 were more effective than BTP2 or expression of the dominant-negative Orai1^E190Q in reducing both Ca²⁺ entry and [Ca²⁺]_i, implicating a non-STIM1/ Orai1 SOCE pathway in resetting resting [Ca²⁺] _i. Indeed, two nonselective cationic channels, TRPC3 and TRPC6, are overexpressed, and [Na]_i is chronically elevated in MH-RyR1 ^R163C muscle cells. [Ca²⁺]_i and [Na ⁺]_i are persistently elevated in vivo and further increased by halothane in MH-RyR1^R163C/WT muscle. These increases are markedly attenuated by local perfusion of Gd⁺³ or GsMTx-4 and completely suppressed by dantrolene. These results contribute a new paradigm for understanding MH pathophysiology by demonstrating that nonselective sarcolemmal cation channel activity plays a critical role in causing myoplasmic Ca ²⁺ and Na⁺ overload both at rest and during the MH crisis.